1. Field of the Invention
This invention relates to use of auxiliary chilled/heated medium, such as water, to produce cooling/heating by interface to a compressor-based refrigerant cycle, such as direct expansion air conditioning. The invention is especially suitable for retrofit to standard direct expansion air conditioning packages, providing the additional feature of utilizing the package evaporator coil for tempering air. Interface of the auxiliary chilled/heated medium may be achieved by a refrigerant-to-water heat exchanger, for example, to transfer thermal energy from a tempered water source to drive a refrigerant phase change and utilizing the thermal energy of the refrigerant phase change in a direct expansion evaporator of a compressor based refrigerant cycle. The thermal energy withdrawal or addition by the auxiliary medium may be utilized in all compressor based refrigerant cycles and may be in place of or in addition to the cooling produced by the compressor-based refrigerant cycle. This invention is applicable to refrigeration and cooling/heating air conditioning applications.
2. Description of the Prior Art
Unitary HVAC systems, sometimes referred to as rooftop, or roof mounted units, are presently commonly used space conditioning systems for commercial facilities. The unitary HVAC systems generally have a single loop refrigerant cycle wherein refrigerant vapor is compressed, the compressed refrigerant vapor is condensed in an ambient air cooled condenser, the liquid refrigerant is passed through an expansion device, and then passed through a direct expansion cooling coil producing a cooling effect to air passing that coil. Present unitary HVAC systems are almost exclusively electrically driven, having electric motor driven compressors. Thermal transfer such as cooling from auxiliary or alternate sources, such as heat-actuated absorption cooling, or alternate cooling or heating sources utilizing thermal energy from natural gas, cogeneration, and the like, has not typically been commercially interfaced with compressor based refrigerant systems because prior proposals have required complex and extensive modification to the compressor based refrigerant systems making the cost extremely high.
Integrated heat exchange systems are taught by U.S. Pat. No. 4,098,092 wherein a heating/cooling heat pump type system is interconnected with an auxiliary water heater wherein thermal energy is recovered from the refrigeration loop to preheat water being fed to a water heater. U.S. Pat. No. 4,199,955 teaches installation of a supplemental hot water heat exchanger between the compressor and condenser of a conventional compressor and condenser of an air conditioning and refrigeration system to utilize the thermal energy of the refrigerant gas thereby improving the overall efficiency of the host air conditioning system. Staged thermal energy recuperation systems are taught by U.S. Pat. No. 4,049,045 wherein the heating and cooling system has thermal storage reservoirs for recuperated thermal energy in each circuit, and U.S. Pat. No. 4,373,346 teaching regulation of water flow so that the refrigerant is precooled to its saturated-vapor state and sub-cooled in the cooling mode and post-heated to at least a saturated-vapor state and sub-cooled when the system is in the heating mode. This is achieved by a separate water loop in sequence through a ground grid heat exchanger/sub-cooler/pre-cooler/condenser in association with the refrigerant cycle. Cooling is taught to be obtained by ambient ground water which cools the system water to approximately 72.degree. F. for introduction to the sub-cooler and the water leaving the sub-cooler at a temperature of about 105.degree. F. to feed the pre-cooler. U.S. Pat. No. 4,179,894 teaches a dual source heat pump system which, in either the heating or cooling mode of operation, will select, for example, either water or air to most efficiently supply the heating or cooling requirements depending upon the relative temperatures of the ambient sources. U.S. Pat. No. 4,281,519 teaches a thermal transfer system which transfers heat energy from a refrigeration loop to a water heating system.